Need help identifying this solid shot ball - Cannon Ball Guy?

This ball is 2.35" diameter and weighs 1.875 pounds. It was found two or three miles north of the Antietam battle field. It was found in the front yard of a period house where I found a cartridge box plate last year, and the front of the house (facing the battle field) has a hole in it where a projectile used to be stuck, but was stolen. The only thing that matches up in the shot charts is a ball from a stand of grape for an 18 pounder gun. But from what I understand, grape was obsolete by the civil war, replaced by canister. So what do we have here?

Depending on the soil conditions of where the cannonball was found , could make a big difference between how quickly it corrodes. There are literally thousands of variables in soil condition that will affect it!